U.S. Pat. No. 4,410,683 to Gale teaches aromatic, melt-processable branched polyesters containing at least three linear polyester chains radiating from a single nucleus wherein the chains comprise hydroxy-acid units derived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. The reference recites that two essential requirements must be met to achieve the desired branching in the polyesters: (i) the main chain monomer contains only functions which are derived from AB-type compounds, i.e., hydroxy acids, rather than diacids and diols which are AA- and BB-type compounds, respectively; and (ii) the nucleus contains only functions which are either all A- or B-type compounds, i.e. , such species must be exclusively polyacids or polyors, respectively. Gale further teaches that failure Lo meet either requirement may result in additional and/or randomized branching.
Branched polyesters as taught by Gale are limited by low molecular weight and lack of networking ability. Low molecular weight, branched polyesters tend to exhibit poor mechanical properties in both the machine and transverse directions, i.e. , weak over all strength. Due to molecular ordering, liquid crystalline polymers generally exhibit good mechanical properties in the direction of molecular ordering, typically, the machine direction. On the other hand, the inability of known branched polyesters to form high molecular weight structures is believed to contribute to their weak over all strength. While known polyesters characterized by a fully networked structure exhibit relatively good mechanical properties in the machine direction and along the transverse direction, these polymers tend to be thermosetting, i.e., a substantially infusible product when cured by heat or other means which make them undesirable for some thermoplastic applications.